Hydrogen Membrane Separator

ABSTRACT

The present application is directed to a hydrophobic membrane assembly ( 28 ) used within a gas-generating apparatus. Hydrogen is separated from the reaction solution by passing through a hydrophobic membrane assembly ( 28 ) having a hydrophobic lattice like member ( 36 ) disposed within a hydrogen output composite ( 32 ) further enhancing the ability of the hydrogen output composite&#39;s ability to separate out hydrogen gas and prolonging its useful life.

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present patent application is a continuation under 35 U.S.C. §120 ofU.S. patent application Ser. No. 14/146,766 entitled “Hydrogen MembraneSeparator” filed on Jan. 3, 2014, which is a continuation of U.S. patentapplication Ser. No. 12/829,827, filed on Jul. 2, 2010 and issued asU.S. Pat. No. 8,636,826 on Jan. 28, 2014, which is acontinuation-in-part of international patent application serial no.PCT/US2009/063108 filed on 3 Nov. 2009 designating the United States,which claims priority to U.S. provisional applications Nos. 61/110,780filed on Nov. 3, 2008 and 61/140,313 filed Dec. 23, 2008. The parentapplications are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The invention relates generally to fuel supplies for fuel cells. Inparticular, the invention relates to hydrophobic membrane assemblies forseparating hydrogen gas from reaction fluids.

BACKGROUND OF THE INVENTION

Fuel cells are devices that directly convert chemical energy ofreactants, i.e., fuel and oxidant, into direct current (DC) electricity.A common fuel for fuel cells is hydrogen gas, which can be stored incompressed form or stored in a hydrogen absorbent material, e.g.,lanthanum nickel alloy, LaNi₅H₆, or other hydrogen absorbent metalhydrides. Hydrogen can also be produced on demand by chemical reactionbetween a chemical metal hydride, such as sodium borohydride, NaBH₄, andwater or methanol.

In a chemical metal hydride reaction, a metal hydride such as NaBH₄,reacts as follows to produce hydrogen:

NaBH₄+2H₂O→(heat or catalyst)→4(H₂)+(NaBO₂)

Half-reaction at the anode:

H₂→2H⁺+2e⁻

Half-reaction at the cathode:

2(2H⁺+2e⁻)+O₂→2H₂O

Suitable catalysts for this reaction include cobalt, platinum andruthenium, and other metals. The hydrogen fuel produced from reformingsodium borohydride is reacted in the fuel cell with an oxidant, such asO₂, to create electricity (or a flow of electrons) and water by-product.Sodium borate (NaBO₂) by-product is also produced by the reformingprocess. A sodium borohydride fuel cell is discussed in U.S. Pat. No.4,261,956, which is incorporated by reference herein in its entirety.The hydrogen produced by chemical metal hydrides may be compressed orstored in a metal hydride hydrogen absorbent material for laterconsumption by a fuel cell.

One disadvantage of the known hydrogen gas generators using chemicalhydride as fuel is that the separation of the hydrogen gas resultingfrom the reaction is not always complete. Over time, water, water vapor,reaction agents, and reaction by-products may pass from the gasgenerator to the fuel cell reducing the fuel cell's efficiency andoperational life.

Accordingly, there is a desire to obtain a hydrogen gas generatorapparatus with a membrane assembly that effectively separates theresulting hydrogen gas from the reaction solutions.

SUMMARY OF THE INVENTION

The present invention is directed to a hydrophobic membrane assembly foruse within a gas-generating apparatus within the fuel supply for a fuelcell. The present invention is also directed to reaction chambers,gas-generating apparatuses, and/or fuel supplies incorporating thehydrophobic membrane assemblies of the current invention.

One aspect of the invention is directed to a gas-generating apparatuswith a reaction chamber; a fuel mixture, which reacts to produce a gasin the presence of a catalyst, within the reaction chamber. The reactionchamber contains a hydrogen output composite of a hydrophobic latticestructure disposed between two gas-permeable, substantiallyliquid-impermeable membranes, and the gas produced by the fuel mixturereaction flows through one or both of the membranes and around thelattice structure. The hydrophobic lattice structure may have a staticcontact angle with water of greater than about 120°, and possibly evengreater than about 150°. Also, the hydrophobic lattice structure mayhave a surface energy of less than about 40 mJ/m², and that surfaceenergy may have a dispersive energy component of less than about 40mJ/m² and a polar energy component of less than about 2.0 mJ/m². Thesurface energy of the hydrophobic lattice structure may also be lessthan about 20 mJ/m², and that surface energy may have a dispersiveenergy component of less than about 20 mJ/m² and a polar energycomponent of less than about 1.0 mJ/m². Further, the surface energy ofthe hydrophobic lattice structure may be less than about 10 mJ/m², andthat surface energy may have a dispersive energy component of less thanabout 10 mJ/m² and a polar energy component of less than about 0.5mJ/m². The hydrophobic lattice structure may also have a contact anglehysteresis measurement of less than about 40°, possibly even less thanabout 20°, or further still less than about 10°.

In this aspect of the invention, the hydrophobic lattice structure maybe a polymer, and the polymer may be poly(tetrafluorethene),polypropylene, polyamides, polyvinylidene, polyethylene, polysiloxanes,polyvinylidene fluoride, polyglactin, lyophilized dura matter, silicone,rubber, and/or mixtures thereof. Preferably, the polymer may bepolyvinylidene fluoride. Alternatively, the hydrophobic latticestructure may be coated with a hydrophobic coating. The hydrophobiccoating may be polyethylene, paraffin, oils, jellies, pastes, greases,waxes, polydimethylsiloxane, poly(tetrafluorethene), polyvinylidenefluoride, tetrafluoroethylene-perfluoroalkyl vinyl-ether copolymer,fluorinated ethylene propylene, poly(perfluorooctylethylene acrylate),polyphosphazene, polysiloxanes, silica, carbon black, alumina, titania,hydrated silanes, silicone, and/or mixtures thereof Preferably, thehydrophobic coating may be poly (tetrafluorethene),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, fluorinatedethylene propylene, poly (perfluorooctylethyl acrylate), orpolyphosphazene. Further still, the hydrophobic lattice structure may becoated with a surfactant, and the surfactant may be perfluorooctanoate,perfluorooctanesulfonate, ammonim lauryl sulfate, sodium laurethsulfate, alkyl benzene sulfonate, a sulfated or sulfonated fattymaterial, salts of sulfated alkyl aryloxypolyalkoxy alcohol,alkylbenzene sulfonates, sodium dodecyl benzenesulfonate,fluorosurfactants, sodium lauryl sulfate, sulfosuccinate blend, sodiumdioctyl sulfosuccinate, sodium sulfosuccinate, sodium 2-ethylhexylsulfate, ethoxylated acetylenic alcohols, high ethylene oxide octylphenols, high ethylene oxide nonyl phenols, high ethylene oxide linearand secondary alcohols, ethoxylated amines of any ethylene oxide length,ethoxylated sorbitan ester, random EO/PO polymer on butyl alcohol, watersoluble block EO/PO copolymers, sodium lauryl ether sulfate, and/ormixtures thereof. The surfactant may optionally include a cross-linkingagent as well.

Additionally, the hydrophobic lattice structure may have a roughenedsurface. Preferably, the hydrophobic lattice structure exhibitsCassie-Baxter behavior.

The gas generating apparatus may have a second hydrophobic latticestructure between the reaction chamber and the hydrogen outputcomposite. Also, the gas generating apparatus may also have a coarsefilter between the catalyst and the hydrogen output composite, andpreferably this coarse filter may be hydrophobic.

Another aspect of the present invention is directed to a gas-generatingapparatus having a reaction chamber, a fuel mixture, which reacts toproduce a gas in the presence of a catalyst, within the reactionchamber. The reaction chamber comprises a hydrogen output compositehaving a lattice structure disposed between two gas-permeable,substantially liquid-impermeable membranes, at least one of which hashad its hydrophobicity enhanced, and the gas produced by the fuelmixture reaction flows through one or both of the membranes and aroundthe lattice structure. Preferably, both gas-permeable, substantiallyliquid-impermeable membranes hydrophobicity may be enhanced. Thehydrophobicity of the gas-permeable, substantially liquid-impermeablemembrane may be enhanced by coating the gas-permeable, substantiallyliquid-impermeable membrane with a hydrophobic coating. The hydrophobiccoating may be polyethylene, paraffin, oils, jellies, pastes, greases,waxes, polydimethylsiloxane, poly(tetrafluorethene), polyvinylidenefluoride, tetrafluoroethylene-perfluoroalkyl vinyl-ether copolymer,fluorinated ethylene propylene, poly(perfluorooctylethylene acrylate),polyphosphazene, polysiloxanes, silica, carbon black, alumina, titania,hydrated silanes, silicone, and/or mixtures thereof. Preferably, thehydrophobic coating may be poly (tetrafluorethene),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, fluorinatedethylene propylene, poly (perfluorooctylethyl acrylate), orpolyphosphazene. Alternatively, the hydrophobicity of the gas-permeable,substantially liquid-impermeable membrane may be enhanced by coating thegas-permeable, substantially liquid-impermeable membrane with asurfactant. The surfactant may be perfluorooctanoate,perfluorooctanesulfonate, ammonim lauryl sulfate, sodium laurethsulfate, alkyl benzene sulfonate, a sulfated or sulfonated fattymaterial, salts of sulfated alkyl aryloxypolyalkoxy alcohol,alkylbenzene sulfonates, sodium dodecyl benzenesulfonate,fluorosurfactants, sodium lauryl sulfate, sulfosuccinate blend, sodiumdioctyl sulfosuccinate, sodium sulfosuccinate, sodium 2-ethylhexylsulfate, ethoxylated acetylenic alcohols, high ethylene oxide octylphenols, high ethylene oxide nonyl phenols, high ethylene oxide linearand secondary alcohols, ethoxylated amines of any ethylene oxide length,ethoxylated sorbitan ester, random EO/PO polymer on butyl alcohol, watersoluble block EO/PO copolymers, sodium lauryl ether sulfate, and/ormixtures thereof. Optionally, the surfactant may include a cross-linkingagent.

Further, the substantially liquid-impermeable membrane may have anexterior surface that has been roughened to enhance its hydrophobicity.Preferably this surface exhibits Cassie-Baxter behavior.

The hydrophobicity of the substantially liquid-impermeable membrane maybe enhanced by about 10%.

A further aspect of the current invention is directed to a gasgenerating apparatus having a reaction chamber, a fuel mixture, whichreacts to produce a gas in the presence of a catalyst, within thereaction chamber. The reaction chamber has a hydrogen output compositewith a lattice structure disposed between two gas-permeable,substantially liquid-impermeable membranes, and the gas produced by thefuel mixture reaction flows through one or both of the membranes andinto the lattice structure. The surface tension of the fuel mixture inthis aspect of the current invention is greater than the surface energyof the gas-permeable, substantially liquid-impermeable membranes. Thesurface tension of the fuel mixture is greater than 73 dynes/cm.Alternatively, the surface tension of the fuel mixture may be at leastdouble that of the surface energy of the gas-permeable, substantiallyliquid-impermeable membrane.

A further aspect of the present invention is directed to a gasgenerating apparatus having a reaction chamber, a fuel mixture, whichreacts to produce a gas in the presence of a catalyst, within thereaction chamber. The reaction chamber has a hydrogen output compositehaving a lattice structure disposed between two gas-permeable,substantially liquid-impermeable membranes, and the gas produced by thefuel mixture reaction flows through one or both of the membranes andinto the lattice structure. In this aspect of the invention, a superacidic filter is located downstream of the lattice structure tosubstantially remove basic contaminants from the produced gas. The superacidic filter may be a perfluorinated sulfonic acid polymer. Also, thesuper acidic filter may remove greater than 90% of the basiccontaminants from the produced gas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith:

FIG. 1 is an exploded view of one embodiment of the inventivehydrogen-generating apparatus;

FIG. 2 is a partial cross-sectional view of the inventivehydrogen-generating apparatus depicted in FIG. 1; and

FIG. 3 is a partial cross sectional view of the inventive hydrogenoutput composite of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in the accompanying drawings and discussed in detailbelow, the present invention is directed to hydrophobic membraneassembly for a fuel supply or gas generator which produces hydrogen foruse in fuel cells.

The fuel supplies used with the membrane assembly contain a fuel mixtureand a catalyst. This fuel mixture is generally the solution formed bydissolving a solid fuel component in a liquid fuel component.

The term “solid fuel” as used herein includes all solid fuels that canbe reacted to produce hydrogen gas, and includes, but is not limited to,all of the suitable chemical hydrides described herein and inWO2010-051557 A1, including lithium hydride, lithium borohydride, sodiumhydride, potassium hydride, potassium borohydride, lithium aluminumhydride, combinations, salts, and derivatives thereof. WO2010-051557 A1is incorporated herein by reference in its entirety. Preferably thesolid fuel component is a chemical metal hydride such as sodiumborohydride. The solid fuel component may include other chemicals, suchas solubility-enhancing chemicals or stabilizers, such as soluble metalhydroxides, and preferably includes sodium hydroxide. Other usablestabilizers include potassium hydroxide or lithium hydroxide, amongothers.

The term “liquid fuel” as used herein includes all liquid fuels that canbe reacted to produce hydrogen gas, and includes, but is not limited to,suitable fuels described herein and in WO2010-051557 A1, includingwater, alcohols and additives, catalysts, and mixtures thereof.Preferably, the liquid fuel, such as water or methanol, reacts with thesolid fuel in the presence of catalyst to produce hydrogen. The liquidfuel may also include additives, stabilizers, or other reactionenhancers, such as sodium hydroxide as a stabilizer, a polyglycol as asurfactant, or many others.

The catalyst may be platinum, ruthenium, nickel, cobalt, and othermetals including those disclosed in WO2010-051557 A1 and derivativesthereof. The preferred catalysts include cobalt chloride or rutheniumchloride, or both. Another preferred catalyst is a compound containingcobalt and boron. In the presence of the catalyst, the fuel mixturereacts to produce hydrogen. A preferred catalyst system is discussed inInternational Application No. PCT/US2009/0069239, which is incorporatedby reference in its entirety.

The gas-generating apparatus of the present invention may include areaction chamber, which may include a first reactant, a second reactantand a catalyst. The first and second reactants can be a metal hydride,e.g., sodium borohydride, and water or methanol. The reactants can be ingaseous, liquid, aqueous or solid form. Preferably, the first reactantis a solid chemical hydride or chemical borohydride and selectedoptional additives and stabilizers, and the second reactant is water ormethanol optionally mixed with selected additives and stabilizers, suchas sodium hydroxide. The catalyst may be platinum, ruthenium, cobalt,nickel, or other metals or compounds such as cobalt chloride orruthenium chloride. Water and stabilized chemical hydride react in thepresence of a catalyst to produce hydrogen gas, which can be consumed bya fuel cell to produce electricity. Alternately, liquid hydrogenperoxide and solid permanganate reactants can be used to produce oxygenusing the gas generating apparatus of the present invention. Anothersuitable reaction to generate oxygen is disclosed in U.S. Pat. No.4,620,970, which is incorporated herein by reference in its entirety.

As used herein, the term “fuel supply” includes, but is not limited to,disposable cartridges, refillable/reusable cartridges, containers,cartridges that reside inside the electronic device, removablecartridges, cartridges that are outside of the electronic device, fueltanks, fuel refilling tanks, other containers that store fuel and thetubings connected to the fuel tanks and containers. While a cartridge isdescribed below in conjunction with the exemplary embodiments of thepresent invention, it is noted that these embodiments are alsoapplicable to other fuel supplies and the present invention is notlimited to any particular type of fuel supply.

The fuel supply used with the membrane assembly of the present inventioncan also be used to produce fuels that are not used in fuel cells. Theseapplications can include, but are not limited to, producing hydrogen formicro gas-turbine engines built on silicon chips, discussed in “HereCome the Microengines,” published in The Industrial Physicist (December2001/January 2002) at pp. 20-25. As used in the present application, theterm “fuel cell” can also include microengines.

The inventive hydrophobic membrane can be used with any known hydrogengenerators. Suitable known hydrogen-generating apparatus are disclosedin commonly-owned, U.S. Pat. Nos. 7,674,540 and 7,481,858, U.S. PatentApplication Publication No. US2006-0174952 A1, International PublicationNo. WO2010-051557 A1 and International Application No.PCT/US2009/0069239 with which the inventive hydrophobic membraneassembly may be used. The disclosures of these references areincorporated by reference herein in their entireties.

FIGS. 1-3 illustrate a representative hydrogen-generating apparatus 10in accordance with the present invention. Hydrogen generating apparatus10, as illustrated, is operated by pushing lock knob 12 inwards ortowards outlet valve 14, which is located on the opposite end ofhydrogen generator 10. As shown, lock knob 12 is attached to seal piston16, which moves the seal 18 towards an open position when lock knob 12is depressed. This releases the solid fuel contained within the chamber20 inside cap 22. The solid fuel then dissolves within liquid fuelpresent within the interior of container 24 to form an aqueous fuelmixture, discussed above. This aqueous fuel mixture contacts a catalystwithin reactor buoy 26 and reacts to produce hydrogen. As described indetail in WO2010-051557 A1, reactor buoy 26 opens and closes dependingon the internal pressure of hydrogen generator 10 and a referencepressure to control access to the catalyst to control the production ofhydrogen. The produced hydrogen gas permeates into membrane assembly 28and is transported out of container 12 and hydrogen generator 10,discussed below.

As illustrated, membrane assembly 28 comprises outer lattice 30 andhydrogen output composite 32. Hydrogen outlet composite 32 comprises inthis preferred embodiment two layers of hydrogen permeable membranes 34positioned on either sides of internal lattice 36. Hydrogen permeablemembranes allow hydrogen to pass through but substantially excludeliquids. Suitable hydrogen permeable membranes include any substantiallyliquid-impermeable, gas-permeable material known to one skilled in theart. Such materials can include, but are not limited to, hydrophobicmaterials having an alkane group. More specific examples include, butare not limited to: polyethylene compositions, polytetrafluoroethylene,polypropylene, polyglactin (VICRY®), lyophilized dura mater, orcombinations thereof Commercially available suitable hydrogen permeablemembranes include GORE-TEX®, CELGARD® and SURBENT® polyvinylidenefluoride (PVDF). Additionally, or alternatively, the hydrogen permeablemembrane may include any of the gas-permeable substantiallyliquid-impermeable materials disclosed in U.S. Pat. No. 7,147,955,incorporated herein by reference.

Hydrogen permeable membranes 34 are preferably sealed together aroundinternal lattice 36 to form the multilayer hydrogen output composite 32.Internal lattice 36 minimizes the possibility that the two hydrogenpermeable membranes 34 would contact each other or seal together tominimize the flow of hydrogen. Outer lattice 30 is used to minimizecontact between hydrogen output composite 32 with container 24, whichcould reduce the flow rate of hydrogen into hydrogen output composite32. Outer lattice 30 and internal lattice 36 are preferably flexible. Ina preferred embodiment, multilayer hydrogen output composite 32 isconstructed as a flat structure, as best shown in FIG. 3, with hydrogenconduit 38 attached to one side of hydrogen output composite 32. Acoarse filter 37, such as a corrugated paper or nonwoven or woven onreactor side of the membrane can be placed on top of the flat structureto minimize the contact between hydrogen output composite 32 and anysolids that may precipitate from the fuel solution. The entire flatstructure can simply be rolled up and inserted into container 24.Hydrogen conduit 38 is in fluid communication with the interior ofhydrogen output composite 32 and with hydrogen chamber 40.

Hydrogen output laminate 32 is connected to valve 14 and comprises threeor more laminate layers. The outermost layers comprise membranes 34permeable to a gas such as hydrogen but impermeable to liquid, and theinner layer comprises a lattice-like material 36 as a support structureto allow gas flow through the membranes 34 to valve 14. Lattice-likematerial 36 may be a solid lattice, a fabric, textile, nylon knit, wick,mesh material, or other gas permeable structure that can serve as a basefor lamination. Laminate 32 serves to filter produced hydrogen gas outof the fuel mixture and convey the produced gas to valve 14. Byconstructing this liquid separator in this manner, instead of using amembrane enclosing a fuel mixture, higher pressures can be used withinthe housing, because laminate 32 is under compression while themembrane, such as membrane/screens 86/84/88 disclosed in grandparentapplication PCT/US 2009/063108 which is previously incorporated byreference, would be under expansion. Laminate 32 has the ability towithstand more compression than the membrane could withstand expansion.Lattice-like material 36 may be stiff or flexible. Alternatively,laminate 32 may be replaced by a lattice-like or fabric material with ahydrogen permeable membrane to either side. Laminate 32 may alsocomprise a pair of screens on the sides of membranes 34 oppositelattice-like material 36.

The hydrogen gas is separated from the reaction solution when it passesthrough hydrogen permeable membranes 34 into the interior of hydrogenoutput composite 32, where the hydrogen passes through and/or alonginternal lattice 36 to hydrogen conduit 38 to flow out of hydrogenoutput composite 32. Hydrogen conduit 38 is connected to hydrogenchamber 40, and hydrogen collects in chamber 40. Hydrogen chamber 40 cancontain a super acid to filter out unwanted alkalis. Outlet valve 14 isconnected to hydrogen chamber 40 and is also connected to a fuel cell(not shown). First relief valve 42 is provided to hydrogen chamber 40 tovent hydrogen when the pressure within chamber 40 is above apredetermined threshold level. Second relief valve 44 is provided tochamber 24 to vent when the pressure in that chamber is above anotherpredetermined threshold level.

Buoy 26 is connected by tube 46 to outside atmosphere so thatatmospheric pressure can serve as the reference pressure, as best shownin FIG. 2. Tube 46 may be rigid and hold buoy 26 vertically or at anangle of about 45°, preferably between about 35° and about 55°. Theseangles preferably allow trapped gas to move away from buoy 26 when buoyopens or closes. Tube 46 preferably is connected to surface channels 48,which are depressions formed on an outside surface of chamber 24.Multiple surface channels 48 ensure that tube 46 remains open toatmosphere even when the user's finger or debris blocks or partiallyblocks tube 46. Channels 48 can be disposed on the bottom of chamber 24,as shown, or on the side of chamber 24.

Outlet valve 14 can be any valve capable of controlling hydrogen flow,and preferably are the valves described in international patentapplication publication nos. WO2009-026441 and WO2009-026439, which areincorporated herein by reference in their entireties. Preferably, outletvalve 14 comprises center post 48, which is substantially immovablerelative to chamber 24, and can be fixedly mounted to the bottom ofchamber 24, as best shown in FIG. 2. Seal 50, which could be an 0-ringor a flat washer, surrounds center post 48 and provides a seal forhydrogen chamber 40. Retainer 52 maintains or locks seal 50 in itsproper place. Other suitable outlet valves include, but are not limitedto, valves disclosed in U.S. Pat. Nos. 7,537,024, 7,059,582, 7,617,842and U.S. published patent applications nos. US2006-0174952 andUS2010-0099009. These references are also incorporated herein byreference in their entireties.

To render outlet valve 14 more difficult to operate by unintentionalusers or to reduce the possibility of connecting hydrogen generator 10to incompatible machineries, a matching pre-pilot blind bore 54 isprovided around outlet valve 14. To open valve 14, a corresponding ormating valve should have a cylindrical member that fits around centerpost 48 and inside retainer 52 to open seal 50 and an annular/concentricmember that fits within pre-pilot bore 54. Other mechanisms to ensuredifficult operation by unintended users and/or incompatible machineriesare disclosed in U.S. published patent application nos. US 2005-0074643,US2008-0145739, US2008-0233457 and US2010-0099009, which areincorporated herein by reference in their entireties.

Generally, lattices 30, 36 can be any lattice-like material and may bestiff or flexible. The lattice material may be a hydrophobic solidlattice, a fabric, textile, nylon knit, wick, mesh material, screen,corrugated shape, or other gas permeable structure that can serve as abase for lamination and prevent the membranes 34 from collapsing on oneanother. Suitable lattice materials including those positioned orinserted within a fuel bladder disclosed in co-owned U.S. Pat. No.7,172,825, which is hereby incorporated by reference in its entirety.Lattice materials inserted into such fuel liner may be made integral tothe wall of the liner. Hydrogen output composite 32 filters producedhydrogen gas out of the fuel mixture and convey the produced gas tohydrogen outlet 38 and to outlet valve 14. By constructing the hydrogenseparator in this manner which is also discussed in WO2010-051557 A1,membrane assembly 28 is inserted in the middle of the solution allowingthe pressure to be equal on both sides with a differential pressureresulting in compression.

The inventors of the present invention observed that after a period oftime liquid fuel and/or liquid byproduct, which contains water, enteredthe hydrogen output composite. The water appeared to contain additives,such as potassium hydride, KOH, or sodium hydride, NaOH, and reactionby-products such as potassium borates, KBO₂, and sodium borates, NaBO₂These contaminants can detrimentally affect the polymer electrolyte orthe MEA of the fuel cell when they pass through outlet valve 14 with thehydrogen gas. After considerable effort and quite unexpectedly, withoutbeing bound to any particular theory, it was determined that lattice 36may have been responsible for the entry of the liquid fuel into hydrogenoutput composite 32. The inventors believe that interior lattice 36 washydrophilic in nature when compared to hydrogen permeable, substantiallyliquid impermeable membranes 34. When interior lattice 36 was in contactwith hydrogen permeable, substantially liquid impermeable membrane 34,it may have caused or encouraged through the process of osmotic dragwater or liquid fuel with the contaminants to go through the pores ofhydrogen permeable, substantially liquid impermeable membrane 34. It isalso believed that the internal pressure of chamber 24, especially whenhydrogen is being produce also encourages liquid fuel to go throughmembranes 34. The liquid fuel with the contaminants can accumulatewithin the hydrogen output composite 32.

The current invention relates to a hydrophobic hydrogen output composite32, and preferably a hydrophobic membrane assembly 28.

The hydrophobicity of a solid (or wettability) depends on the forces ofinteraction between water, the surface and the surrounding air. See J.C. Berg, “Wettability”, Marcel Dekker, New York, 1993 and A. W. Adamson,“Physical Chemistry of Surfaces”, Wiley. The forces of interactionbetween water and air are surface tension, γ_(LV). Similarly, a surfaceenergy, γ_(SV), is defined as the forces between a solid and thesurrounding air and interface tension, γ_(LS), is defined as the forcesbetween the solid and water. For a drop of liquid in equilibrium on asurface, Young's equation stipulates that γ_(SV)−γ_(LS)=γ_(LV) cos θ,where θ is the contact angle of the drop of water in relation to thesurface. Young's equation also shows that, if the surface tension of theliquid is lower than the surface energy, the contact angle is zero andwater, wets the surface. Additionally, the water may partially wet thesurface (contact angle greater than 0°). If the contact angle is between0° and 90° the surface is considered hydrophilic; and if the contactangle is greater than 90° the surface is considered hydrophobic. And incertain instances, super-hydrophobic materials, such as lotus leaves,have been noted as having a static water contact angle above 150°. Inparticular, the static contact angle of a substrate can be measuredusing a contact angle goniometer and can be measured by methods known tothose skilled in the art including the sessile drop method (static anddynamic), Wihelmy method (dynamic and single-fiber), and powder contactangle method.

The surface energy of a solid, the excess energy available at thesurface of a solid as compared to its bulk, is determinative of thesolids hydrophilic or hydrophobic state. Matter seeks to be in a lowenergy state and chemical bonds reduce energy. Thus, surfaces that havehigh surface energies tend to be hydrophilic since those surfaces willinitiate binding with the hydrogen molecules within water. Hydrophobicmaterials have lower surface energies and are unable to form hydrogenbonds with water, and water repels the hydrophobe in favor of bindingwith itself. Young's equation illustrates this point.

The surface energy of a solid depends on several factors (J. P. Renaudand P. Dinichert, 1956, “Etats de surface et etalement des huilesd'horlogerie”, Bulletin SSC III page 681): the chemical composition andcrystallographic structure of the solid, and in particular of itssurface, the geometric characteristics of the surface and its roughness(and therefore the defects and/or the state of polishing), and thepresence of molecules physically adsorbed or chemically bonded to thesurface, which can easily mask the solid and significantly modify itssurface energy.

The Owens Wendt Theory, also known as the harmonic mean method, can beused to measure the surface energy of a solid. Owens, D. K.; Wendt, R.G. “Estimation of the surface force energy of polymers”, J. Appl. Polym.Sci. 1969, 51, 1741-1747. This theory posits that the surface energy ofthe surface is the sum of its polar and dispersive components. The polarcomponent accounts for dipole-dipole, dipole-induced, hydrogen bondingand other site specific interactions between a solid and liquid. Thedispersive component accounts for surface interactions from Van derWaals and other non-site specific interactions between a solid andliquid. The model is based on two fundamental equations which describethe surface interactions between solids and liquids: Good's Equation(σ_(SL)=σ_(S)+σ_(L)−2(σ_(L) ^(D)σ_(S) ^(D))^(1/2)−2(σ_(L) ^(P)σ_(S)^(P))^(1/2))and Young's Equation (σ_(S)=σ_(SL)+σ_(L) cos θ). Thedispersive component of the surface tension of the wetting liquid isσ_(L) ^(D); the polar component of the surface tension of the wettingliquid is σ_(L) ^(P); the dispersive component of the surface energy ofthe solid is σ_(S) ^(P); and the polar component of the surface energyof the solid is σ_(S) ^(P). Combining Good's and Young's equationproduces the following equation: σ_(L) (cos θ+1)/2 (σ_(L)^(D))^(1/2)=(σ_(S) ^(P))^(1/2)((σ_(L) ^(P))^(1/2)/(σ_(L) ^(D)))+(σ_(S)^(D))^(1/2). The equation has the linear form of y=mx+b, whereby y=σ_(L)(cos θ+1)/2 (σ_(L) ^(D))^(1/2); m=(σ_(S) ^(P))^(1/2); x=(σ_(L)^(P))^(1/2)/(σ_(L) ^(D)); b=(σ_(S) ^(D))^(1/2).

The polar and dispersive components of the wetting liquids are known inthe literature. A series of replicate contact angles are measured foreach of at least two wetting liquids that include, but are not limitedto, diiodomethane, benzyl alcohol, ethylene glycol, formamide and water.The y′s are plotted as a function of x′s and the polar component of thesurface energy, σ_(S) ^(P), is equivalent to the square root of theslope, m, and the dispersive component of the surface energy, σ_(S)^(D), is equivalent to the square root of the y-intercept, b.

Additionally, the surface energy of a solid may be measured usingcontact angle hysteresis. To make this measurement a pipette injects aliquid onto a solid, and the liquid forms a contact angle. The pipettethen injects more liquid, the droplet will increase in volume and itscontact angle will increase, but its three phase boundary will remainstationary until it suddenly advances outward. The contact angle thedroplet had immediately before advancing outward is termed the advancingcontact angle. The receding contact angle is now measured by pumping theliquid back out of the droplet. The droplet will decrease in volume, thecontact angle will decrease, but its three phase boundary will remainstationary until it suddenly recedes inward. The contact angle thedroplet had immediately before receding inward is termed the recedingcontact angle. The difference between advancing and receding contactangles is termed contact angle hysteresis and can be used tocharacterize surface heterogeneity, roughness, mobility, andwettability. Preferably the contact angle hysteresis should berelatively small for a hydrophobic surface; and for a super hydrophobicsurface should be less than 5°.

The hydrophobic membrane assembly 28 of the current invention preferablycomprises a hydrophobic interior lattice 36 and optionally hydrophobicouter lattice 30. Additionally, the hydrophobicity of membrane 34 may beincreased, and/or the surface tension of the reaction solution withrespect to the surface of membrane 34 may be increased.

In accordance with one embodiment of the invention, the lattice-likematerial is made of hydrophobic materials. A hydrophobic materialsuitable for the current invention may be determined by at least one, ormore, of the following measures: static water contact angle, surfaceenergy, and contact angle hysteresis. If the static water contact angleis used, the static water contact angle should be greater than 90°,preferably it is greater than 120°, and most preferably greater than150°. If surface energy is used, the surface energy of the latticematerials 30, 36 should be less than 40 mJ/m², more preferably less than20 mJ/m², and most preferably less than 10 mJ/m². The surface energiesmay be further evaluated on their dispersive and polar energycomponents. In particular, the polar energy component of the surfaceenergy may be less than about 5%, less than about 2.5%, less than about1%, preferably less than 0.4%, and most preferably less than 0.1%. Forexample in the instance where the surface energy is less than 40 mJ/m²,preferably the dispersive energy component is less than 40 mJ/m² and thepolar energy component is less than 2.0 mJ/m². Similarly, where thesurface energy of lattice 36, 30 is less than 20 mJ/m², preferably thedispersive energy component is less than 20 mJ/m² and the polar energycomponent is less than 1 mJ/m². Properties of Polymers by D. W. VanKrevelen (Elsevier 1990) disclose various polymers, their surfaceenergies, and the dispersive and polar components of their surfaceenergies and are hereby incorporated in its entirety by reference. Also,where the surface energy of lattice 36, 30 is less than 10 mJ/m²,preferably the dispersive energy component is less than 10 mJ/m² and thepolar energy component is less than 0.5 mJ/m². Where the measure iscontact angle hysteresis, the measurement should be less than about 40°,more preferably less than about 20°, most preferably less than about10°. Given that hydrophobic membrane assembly 28 is submerged in anaqueous solution, the surface energy and contact angle hysteresismeasurements are the preferred determinants of whether a material can beconsidered hydrophobic.

Preferably, the lattice 36, 30 is as hydrophobic as the membrane 34. Asnoted above, Cellgard™ is an example of a material suitable for use asmembrane 34 and has a contact angle of about 120°, a surface energy ofabout 22.04 (±0.16) mJ/m² with a dispersive energy component of about22.00 (±0.15) mJ/m² and a polar energy component of about 0.04 (±0.01)mJ/m², and a contact angle hysteresis measurement of about 30°. Morepreferably, lattice 36, 30 is more hydrophobic than membrane 34, i.e.lattice 36, 30 has a higher static contact angle measurement, a surfaceenergy that is less than the surface energy of membrane 34, and/or acontact angle hysteresis measurement that is less than the contact anglehysteresis measurement for membrane 34.

Suitable hydrophobic materials for the manufacture of the latticeinclude hydrophobic substrates such as ceramics, plastics, polymers,glasses, fibers, nonwovens, wovens, textiles, fabrics, carbon and carbonfibers, ion exchange resins, metals, alloys, wires, and meshes. It ispreferred, that the hydrophobic materials be compatible with thereaction solution and not inhibit the ability of hydrogen outputcomposite 32 to allow hydrogen gas to pass through. Suitable hydrophobicmaterials include, but are not limited to, hydrophobic polymericmaterials such as poly(tetrafluorethene) (PTFE), polypropylene (PP),polyamides, polyvinylidene, polyethylene, polysiloxanes, silicone,rubber, polyglactin (VICRY®), lyophilized dura mater, or combinationsthereof. Preferably, the hydrophobic material is PTFE better known asTEFLON® sold by Dupont. More preferably, materials suitable for membrane34, such as, GORETEX®, CELGARD® and SURBENT® may be used as wellprovided that internal lattice 36 and membrane 34 will not seal togetheran impede the flow of hydrogen if they are made of the same material.Additionally, superhydrophobic polymeric materials including but notlimited to superhydrophobic linear low density polyethylene as describedin Yuan et al. “Preparation and characterization of self-cleaning stablesuperhydrophobic linear low-density polyethylene.” Sci. Technol. Adv.Mater. 9 (2008), may be used as well.

In an alternative embodiment, the lattice-like materials may be madefurther hydrophobic or alternatively a hydrophilic base material may bemade hydrophobic through coating with a hydrophobic coating or superhydrophobic coating. Solutions used to coat the lattice like materialmay include, but are not limited to, polyethylene, paraffin, oils,jellies, pastes (TEFLON® and carbon paste), greases, waxes,polydimehtylsiloxane, PTFE, polyvinylidene fluoride,tetrafluoroethylene-perfluoroalkyl vinyl-ether copolymer, fluorinatedethylene propylene (FEP), poly(perfluorooctylethylene acrylate) (FMA),polyphosphazene, polysiloxanes, silica, carbon black, alumina, titania,hydrated silanes, silicone, and/or mixtures thereof. Preferably, highlywater repellent material such as PTFE,tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),fluorinated ethylene propylene (FEP), poly (perfluorooctylethylacrylate) (FMA), polyphosphazene, and/or mixtures thereof, is used tocoat the lattice like material 36, 30. Methods of formingsuperhydrophobic coatings, and applying superhydrophobic coatings suchas those disclosed in International Publication Nos. WO 98/42452 and WO01/14497, hereby incorporated by reference, are also contemplated.

Also, processes that can be used to apply the above-noted hydrophobiccoatings are well known in the art and include chemical and physicalcoating processes. For example, the compositions can be used withsolvents such as N-methyl-2-pyrrolidone and dimethyl acetamide, or as anemulsion. The coating process can be performed by any method includingbrush application, spray application, dipping, and screen printing. Thecoatings may also be done using the Sol-Gel processes. In a Sol-Gelprocess, the surface is coated with hydrophobic nano-particles which areincluded within a polymer network. The coatings are composite materials(nano-composites) with organic and inorganic components which areproduced by using Sol-Gel processes. The coating is applied by usingsimple dipping or spraying processes followed by a hardening process.

Additionally, a hydrophobic coating may be introduced onto the surfaceof lattice like material 36, 30 by plasma treatment. By this means, thehydrophobic layer may be formed at a desired thickness. By applying, forexample, CF₄ plasma treatment to the surface, water repellency isapplied to the surface of the base material.

In addition to the above-noted hydrophobic coatings, surfactants,including, but not limited to, soaps, detergents, and wetting agents maybe applied to the surface of lattice like material 36, 30. Surfactantsare amphiphilic: the surfactant particles contain a hydrophobic tail andhydrophilic head. Without being bound to any particular theory, it isbelieved that a surfactant coating on the surface of the lattice likematerial 36, 30 will form an additional barrier. Specifically, thesurfactant particles will orient themselves so that their hydrophobictails are in contact with the surface of the lattice like material andtheir hydrophilic heads are in contact with the liquid, therebyisolating the surface of lattice like material 36, 30 from the liquidfuel. Surfactants for use as coatings include, but are not limited to,ionic (anionic, cationic, or zwitterionic) or nonionic surfactants.Surfactants include, but are not limited to, perfluorooctanoate,perfluorooctanesulfonate, ammonim lauryl sulfate, sodium laurethsulfate, alkyl benzene sulfonate, a sulfated or sulfonated fattymaterial, salts of sulfated alkyl aryloxypolyalkoxy alcohol,alkylbenzene sulfonates, sodium dodecyl benzenesulfonate (RhodacalLDS-10 surfactant from Rhone Poulenc), fluorosurfactants (FluoradFC-170C surfactant available from 3M), sodium lauryl sulfate(commercially available as Sipon UB), sulfosuccinate blend (commerciallyavailable as Aerosol OTNV), sodium dioctyl sulfosuccinate (commerciallyavailable as Aerosol TO from Cytec Industries), sodium sulfosuccinate,or sodium 2-ethylhexyl sulfate (commercially available as Rhodapon BOS);ethoxylated acetylenic alcohols, such as Surfynol CT-111, high EO(ethylene oxide) octyl phenols, such as Iconol OP-10 and Triton CF-87;high EO nonyl phenols, such as Igepal CO-730 (NP-15); high EO linear andsecondary alcohols, such at Tergitol 15-S-12 (secondary), Tergitol TMN10 (90%) (linear), Neodol 1-9(linear), Neodol 25-12 (linear), andMazawet 36 (Decyl random EO/PO; ethoxylated amines of any EO length,such as Chemeen T-10 (tallow, 10E0), Chemeen T-15, Chemeen C-15 (Coco.15 EO), Trymeen 6640A, Tomah E-18-15 (18C, 15E0), Tomah E-18 10, andTomah E-S-15 (Soya); ethoxylated sorbitan ester, e.g., POE 20 SorbitanMonoleate (BASF T-Maz 80); random EO/PO polymer on butyl alcohol, suchas Tergitol XJ, Tergitol XD, Tergitol XH, and Tergitol XH; other watersoluble block EO/PO copolymers, such as Pluronic L61LF, Pluronic L101,Pluronic L121, and Plurafac LF131, and Norfox LF-30 and LF-21, sodiumlauryl ether sulfate and/or mixtures thereof. Further, the coatingsolutions of surfactants may include cross linking agents to increasethe longevity and robustness of the surfactant coating. The lattice likematerial 36, 30 may be coated using methods described above.

Further, it is known that microstructuring a surface amplifies thenatural tendency of a surface (Wenzel's equation), and in certaininstances if the roughened surface can entrap vapor (such as air orother gases) the hydrophobicity of the surface may be further enhancedbeyond that achieved in the Wenzel state (Cassie-Baxter equation). Thus,a hydrophobic surface becomes more hydrophobic when it ismicrostructured or roughened. A critical roughness factor, rc=−1/cos θ,provides insight as to when a roughened surface will exhibit Wenzel orCassie-Baxter behavior. Preferably, roughened lattice like material 36,30 exhibits Cassie-Baxter behavior. Further it may be useful to providelattice like material 36, 30 with a dual/hierarchical multiscale surfacestructure as disclosed in Naik, V., Mukherjee, R., Majumdar, A., Sharma,A., “Super functional materials: Creation and control of wettability,adhesion, and optical effects by meso-structuring of surfaces”, CurrentTrends in Science, Bangalore, Indian Academy of Sciences, pp. 129-148,2009, hereby incorporated by reference. In addition to the above-notedmeans of making lattice-like material 36, 30 hydrophobic, it is alsocontemplated that the surface of lattice like material 36, 30 can bemicrostructured using methods known in the art including, but notlimited to, top down approaches such as direct replication of naturalwater repellent surfaces via molding and templating includingnanocasting, replica molding using moldable polymers, and/or creatingpatterns or textures on surfaces using micromachining, lithography(photolithographic, soft lithographic (nano imprint lithography,capillary force lithography, micromolding in capillaries, microtransfermolding), e-beam lithography), and plasma etching; as well as bottom upapproaches such as chemical bath deposition, chemical vapor deposition,electrochemical deposition, layer-by-layer deposition via electrostaticassembly, colloidal assembly, sol-gel methods, nanosphere lithography,water droplet condensation induced pattern formation, and/ormicroabrasion. Preferably the microstructuring is done prior to coatingwith a hydrophobic material, but may be done following coating dependingupon the thickness of the coating.

The above disclosure relates to lattice like material 36, 30, but itwill be appreciated that the same principles and processes can beapplied to other parts of hydrogen generator 10, such as coarse filter37.

In an alternative embodiment, the hydrophobicity of membrane 34 isenhanced. This may be accomplished by coating membrane 34 with ahydrophobic coating, microsurfacing/roughening the surface of membrane34, and/or coating the membrane 34 with a surfactant, as noted above.Further it has been noted that superhydrophobic surfaces are resistantto attachment by water-soluble electrolytes, such as acids and alkalies,and thus preferably the surface of membrane 34 is coated withsuperhydrophobic compounds or microstructured in accordance with thedisclosure above. It is preferred that after the above noted treatmentsthat the hydrophobicity of the membrane 34 is increased by at least 10%.In particular, the surface energy of membrane 34 decreases by at leastabout 10%, more preferably after modification membrane 34 has a surfaceenergy of less than about 20 mJ/m² with a dispersive energy component ofless than about 20 mJ/m² and a polar energy component of less than about1 mJ/m², and/or a contact angle hysteresis measurement of less than 30°.Most preferably, the membrane 34 has a surface energy of less than about10 mJ/m² with a dispersive energy component of less than about 10 mJ/m²and a polar energy component of less than about 0.5 mJ/m², and/or acontact hysteresis measurement of less than about 10°. The membrane maybe coated with a hydrophobic coating or surfactant, and/or microsurfacedin addition to or alternatively to the hydrophobic lattice like material36, 30, as noted above.

One of ordinary skill in the art will appreciate that hydrophobicmembrane assembly 28 of the current invention may include three or morelayers. FIG. 3 provides a diagram of hydrogen output composite 32consisting of two membranes 34 and a lattice like material 36. However,hydrophobic membrane assembly 28 may have one or more hydrogen outputcomposites 32 with one or more lattice like materials separating thevarious membrane layers of the hydrogen output composites. Preferably,the membrane assembly may be multilayered to maintain the hydrophobicnature of the membrane assembly for the useful life of the gasgenerating cartridge, such that if an outer layer may lose itshydrophobicity one of the inner layers will continue to preventcontaminants from being transported to the fuel cell.

Additionally, the lattice like materials in the hydrogen outputcomposites may be cut at a bias (at an angle so that individual grids ofthe lattice resemble diamonds instead of boxes) so that if any water orwater vapor enters into the hydrogen output composite it is guided awayfrom output valve 14. The form of hydrophobic membrane assembly 28 maybe further adapted to a similar use in other fuel supply devices. Forexample, the membrane 34 may be sandwiched between two or more latticelike materials 36, 30 to provide rigidity in arrangements where themembrane is not under compression forces and there is a risk thatexpansion forces may rupture the membrane 34.

Further, as indicated above, a liquid wets a surface when the surfacetension of the liquid is less than the surface energy of the solid.Therefore, in order to enhance the hydrophobic nature of the membraneassembly 28, it may be desirable to increase the surface tension of thereaction solution. Surface tension is a property of the surface of aliquid, and is what causes the surface portion of liquid to be attractedto another surface, such as that of another portion of liquid. Surfacetension is caused by cohesion (the attraction of molecules to likemolecules). Since the molecules on the surface of the liquid are notsurrounded by like molecules on all sides, they are more attracted totheir neighbors on the surface. Thus, if the surface tension of thereaction solution is increased the solution will be less likely to breakthe surface tension and traverse hydrogen output composite 32.

This may be accomplished in two manners. First, certain surfactantsadded to the reaction solution such as alcohol-based compositions, usedas anti-freezing agents, or glycols used as anti-foam agents should beused sparingly or replaced given that surfactants depress the surfacetension of a solution. Alternatively, inorganic salts, such as sodiumchloride, may be used to raise the surface tension of the solution.However, care must be taken that the inorganic salt will not interferewith the ongoing reaction between sodium borohydride and water.

The surface tension of the reaction solution should be greater than 73dyne/cm, preferably greater than 100 dyne/cm. Alternatively, the surfacetension of the reaction solution/fuel mixture should be at least twicethe surface energy of the membrane 34, and more preferably the surfacetension of the reaction solution/fuel mixture should be at least 2.5times greater than the surface energy of the membrane 34.

As noted above, contaminants may foul the polymer electrolyte membraneof the fuel cell. In particular, basic (alkali) contaminants are knownto permeate and reduce the effectiveness of polymer electrolyte membraneby neutralizing the highly acidic perfluorinated sulfonic acid polymer(NAFION® available from Dupont) used as the polymer electrolytemembrane. As a further precaution against contaminants, especiallyalkali contaminants such as sodium or potassium borate or sodiumhydroxide, exiting fuel system 10 and fouling the fuel cell, it ispreferable to locate a super acidic filter downstream of the hydrogenoutput composite 32. Preferably, this filter may be located withinhydrogen conduit 38, hydrogen chamber 40, valve 14, within the tubing orconduit from fuel supply 10 to the fuel cell (not shown), and/or withina separate housing located between fuel supply 10 and the fuel cell. Ifthe filter is intended to be replaceable, it is preferred that it beincorporated into the separate housing or within detachable elements ofthe fuel supply or the fuel cell.

The super acidic filter is made from an acidic material that in oneembodiment is substantially the same material as the polymer electrolytemembrane, i.e. NAFION®. Since the super acidic filter of the currentinvention is located upstream of the MEA, the basic contaminants wouldbe attracted to the filter and be removed from the hydrogen gas beforethe hydrogen gas reaches the MEA. The filter material can also be madefrom sulfonated cation-exchange ion exchange resins that are stronglyacidic such as Amberlyst® from Rohm & Haas. Similar acidic filters aredisclosed in U.S. Pat. Nos. 7,329,348 and 7,655,147, which areincorporated herein by reference in their entireties.

In the present embodiment, the polymer may be present as a continuoussheet (woven or non-woven), web, screen, matrix, foam, and/or gel; oralternatively may be present as discrete pieces such as nanoparticles,microbeads, and/or powders, provided that they do not impede the flow ofhydrogen gas from the fuel supply 10 to the fuel cell. Filters formed ofdiscrete pieces may be preferred given the increased surface areaprovided by such filter arrangements. The discrete pieces of the filtermay be bound together using suitable binders that are resistant tohydrogen gas and potential contaminants. Alternatively, instead of abinder, the filter material can be contained within an open meshfuel-resistant grid such as the matrix disclosed in U.S. Pat. No.7,172,825, which is incorporated by reference in its entirety. Further,as noted above the acidic filter material may be contained within aseparate housing, preferably made of materials resistant to hydrogen gasand potential contaminants, the separate housing may contain screens atan entrance port and an exit port to prevent the filter material fromescaping the housing and to act as a diffuser to slow down the flow forion exchange to take place. Further, the density and permeability of theacidic filter material determines the flow characteristics of thehydrogen gas through the super acidic filter.

The basic contaminants contained within the hydrogen gas are absorbedor, attracted to the acidic filter material downstream of the hydrogenoutput composite 32 so that the hydrogen gas exiting the acidic filterhas less basic contaminants than the hydrogen gas that entered theacidic filter. The acidic filter should substantially remove all basiccontaminants from the hydrogen gas. About 90% of the basic contaminantsmay be removed, more preferably about 95% of the basic contaminants maybe removed, and most preferably about 99% of the basic contaminants maybe removed.

One means of monitoring the removal of basic contaminants known to thoseskilled in the art, includes but is not limited to, monitoring the pHlevel of the hydrogen gas. Although pH is the measure of acidic/basicnature of a solution it may be adapted to gases by exposing a moistenedmaterial, such as a cloth or paper, to the gas and then testing the pHof the exposed moistened material. The pH of the hydrogen gas may act asa further indicator of the removal of basic contaminants, the pH of thehydrogen gas exiting the acidic filter should be 7, neutral, indicatingthe removal of all basic contaminants.

In accordance with another aspect of the present invention, a sensor maybe provided to ascertain the effectiveness of the acidic filter and todetermine when the acidic filter should be replaced. The sensor may bearranged as disclosed in the '348 and '147 patents discussed above. A pHsensor may preferably be located downstream of the acidic filter andupstream of the MEA either within fuel supply 10 (hydrogen chamber 40and/or valve 14), a conduit, tubing or passage, from fuel supply 10,within a separate housing that may contain acidic filter, or within thefuel cell. The pH sensor may simply consist of a damp litmus paper thatchanges color in response to the presence of a base placed within thefluid flow of the hydrogen gas that can be viewed from a transparentwindow in the fuel cell, separate housing and/or conduit to the fuelcell. A transformation in color of the litmus paper would be indicativeof the need to replace the acidic filter, or fuel supply 10, where theacidic filter is integral to fuel supply 10. Further, the pH sensor maybe electric in nature and connected to a controller, and is readable bythe controller. The controller would periodically read the pH sensor,the controller displays a message or other signal such as a visual oraudible signal, to the user to change the acidic filter, possibly at thenext refill of fuel supply 10.

Co-owned and concurrently filed United States Patent Applicationentitled “Gas Generator with Starter Mechanism and Catalyst Shield” andhaving attorney docket number BIC-129 is hereby incorporated byreference in its entirety.

One of ordinary skill in the art will appreciate that the hydrophobicmembrane assembly of the present invention may be applied to other gasgenerating fuel supplies aside from the above disclosed chemical hydridesystem provided that the hydrogen gas needs to be separated from anaqueous solution. Other embodiments of the present invention will beapparent to those skilled in the art from consideration of the presentspecification and practice of the present invention disclosed herein. Itis intended that the present specification and examples be considered asexemplary only with a true scope and spirit of the invention beingindicated by the following claims and equivalents thereof.

1-43. (canceled)
 44. A gas-liquid separation apparatus comprising: ahousing containing a mixture of liquid and gas and gas output compositecomprises at least two gas-permeable, substantially liquid-impermeablemembranes and a lattice structure separating the two membranes whereinthe gas flows through at least one membrane into the gas outputcomposite to an outlet.
 45. The gas-liquid separation apparatus of claim44, wherein in the lattice structure is hydrophobic.
 46. The gas-liquidseparation apparatus of claim 44, wherein the gas comprises hydrogen.47. The gas-liquid separation apparatus of claim 44, wherein the gascomprises oxygen.
 48. The gas-liquid separation apparatus of claim 44,wherein the gas output composite is flexible.
 49. The gas-liquidseparation apparatus of claim 48, wherein the gas output composite iscapable of being rolled when positioned within the housing.
 50. Thegas-liquid separation apparatus of claim 44, wherein the membranes aresealed around at least one edge of the lattice.
 51. The gas-liquidseparation apparatus of claim 44 further comprising an outer lattice.52. The gas-liquid separation apparatus of claim 51, wherein the outerlattice is positioned between the housing and the gas output composite.53. The gas-liquid separation apparatus of claim 44, wherein at least aportion of the gas output composite is a laminate.
 54. The gas-liquidseparation apparatus of claim 44, wherein the lattice structure isintegral with at least a portion of one membrane.
 55. A gas outputcomposite adapted for use with a gas-liquid separation apparatus,wherein the gas output composite comprises: a lattice structureseparating two gas-permeable, substantially liquid-impermeable membranesand the gas output composite is sized and dimensioned to be positionedinside a housing of the gas-liquid separation apparatus, which containsa mixture of liquid and gas and wherein the gas flows through one orboth of the membranes and around the lattice structure to an outlet ofthe gas-liquid separation apparatus, wherein at least a portion of thegas output composite is a laminate.
 56. The gas output composite ofclaim 55, wherein in the lattice structure is hydrophobic.
 57. The gasoutput composite of claim 55, wherein the gas output composite isflexible.
 58. The gas output composite of claim 57, wherein the gasoutput composite is capable of being rolled when positioned within thehousing of the gas-liquid separation apparatus.
 59. The gas outputcomposite of claim 55, wherein the membranes are sealed around at leastone edge of the lattice.
 60. The gas output composite of claim 55,wherein at least a portion of the gas output composite is a laminate.61. The gas output composite of claim 55, wherein the lattice structureis integral with at least a portion of one membrane.